Today, there are many prospective applications for a high-density multi-electrode biocompatible implant. One of the most important is for a cochlear implant. The cochlea is a snail shaped organ of the inner ear that translates sound waves into bioelectrical nerve impulses. A cochlear implant, by directly electrically stimulating the cochlea can effect hearing restoration in persons otherwise completely deaf and for whom other methods of hearing restoration would be ineffective. Compared to the cochlea, however, which includes approximately 30,000 receptive nerve endings, currently available cochlear implants are crude devices, capable of stimulating the cochlea with a degree of selectivity far beneath what the cochlea is capable of accommodating. Accordingly, in order to effect a more complete hearing restoration, cochlear implants having a higher density of precisely positioned electrode contact points are needed.
Because the cochlea has so many more sensing sites than an implant could possibly have electrode contact points, it is desirable to stimulate the cochlea at points between electrode contact points. This can be effected by xe2x80x9cfield shaping,xe2x80x9d in which neighboring electrode contact points are separately controlled to form an electric field that has its maximum at a desired cochlear stimulation point. Unfortunately, in order to perform field shaping it is generally desirable to have electrode contact points that are spaced apart by no more than a few hundred um. Achieving this fine spacing of electrode contact points has proven a challenge to researchers.
The cochlea is not the only site within the body where a high-density implant could be of use, however. The brain, the retina and the heart are just a few other sites within the body where such an implant could be used. Some implants may have to operate for many years without failure. Unfortunately, providing such an implant proves to be quite difficult in practice.
Among the challenges encountered in the construction of an implant having a large number ( greater than 30) of closely spaced ( less than 100 um) and precisely positioned electrode contact points is the problem of decomposition in the body due to attack by the body""s interstitial fluid (ISF). Any seam in an implant will be attacked by ISF and may eventually come apart. Because of this, it is extremely important that biocompatible materials be used throughout an implant. Moreover, the more that an implant can take the form of a seamless, unitary whole the longer an implant can be expected to last within the body. This requirement conflicts with the greater level of complexity desired of implants.
Researchers at the University of Michigan have designed one type of probe that is currently under test. This probe is made by micro machining a silicon substrate using photolithographic techniques in order to achieve accurate positioning of closely spaced electrode contact points. Unfortunately the materials used are stiff and brittle. Accordingly this probe is not well suited for an application that requires flexibility, such as a cochlear implant.
Additionally, multilayer printed circuit board (PCB) technology has advanced so that multilayer structures having traces on the order of microns thick are now available. There are a number of reasons, however, why this technology has, in general, not been applied to the biomedical arena. First, many of the materials used in PCB manufacture are not biocompatible, or degrade after implantation. Second, even flex circuits made from polyimide, a flexible dielectric, typically do not have the degree of flexibility necessary to facilitate the construction and placement of a cochlear implant.
Accordingly, there is a long-standing, unresolved need for a biocompatible, long-term implant that can precisely stimulate a sensory bodily organ, such as the cochlea.
In a first separate aspect, the present invention comprises a bio-implant having a length and a proximal and a distal end. The bio-implant has at least two lamina of dielectric material joined together, thereby defining a boundary and also defining a side surface that is intersected by this boundary. In addition, at least one set of conductors is interposed between the two laminae and extend lengthwise from the proximal end toward the distal end, each one of the set of conductors being terminated adjacent to the side surface to form a set of conductor terminations. Further a set of electrode contact points are constructed on the side surface, with each electrode contact point contacting one of said conductor terminations.
In a second separate aspect, the present invention is a method of constructing a bio-implant having a length and a proximal and a distal end. The method requires a first and second laminae of dielectric material, each of these laminae defining a top surface, a lamina side surface, and a proximal end and a distal end. Also required are at least one set of conductors positioned on the top surface of the first lamina, the conductors extending lengthwise from the proximal end toward the distal end, each one of the set of conductors being terminated adjacent to the side surface to form a set of conductor terminations. The second lamina is joined to the first lamina about the set of conductors, thereby defining a boundary and also defining a joined side surface that is intersected by the boundary. Next, a set of electrode contact points is constructed on the joined side surface, each electrode contact point contacting one of the conductor terminations.
The foregoing and other objectives, features and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.